Spin-orbit torque type magnetization rotational element, spin-orbit torque type magnetoresistance effect element, and magnetic memory

ABSTRACT

A spin-orbit torque type magnetization rotational element includes; a spin-orbit torque wiring that extends in a first direction; a first ferromagnetic layer that is laminated in a second direction intersecting the spin-orbit torque wiring; and a first nonmagnetic metal layer and a second nonmagnetic metal layer that are connected to the spin-orbit torque wiring at positions flanking the first ferromagnetic layer in the first direction in a plan view from the second direction, wherein the gravity center of the first ferromagnetic layer is positioned on a side closer to the first nonmagnetic metal layer or the second nonmagnetic metal layer than is a reference point located at the center between the first and second nonmagnetic metal layers in the first direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-002187, Jan. 10, 2018; the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a spin-orbit torque type magnetizationrotational element, a spin-orbit torque type magnetoresistance effectelement, and a magnetic memory. Priority is claimed on Japanese PatentApplication No. 2018-002187, filed Jan. 10, 2018 in Japan, the contentof which is incorporated herein by reference.

BACKGROUND ART

Giant magnetoresistance (GMR) elements configured of a multilayer filmincluding a ferromagnetic layer and a nonmagnetic layer and tunnelmagnetoresistance (TMR) elements using an insulating layer (a tunnelbarrier layer or a barrier layer) as the nonmagnetic layer are known.These have attracted attention as elements for magnetic sensors,high-frequency components, magnetic heads, and nonvolatile random accessmemories (MRAM).

An MRAM reads and writes data using a characteristic that an elementresistance of a GMR element or a TMR element changes when magnetizationdirections of two ferromagnetic layers sandwiching an insulating layerchange. As a writing method of an MRAM, a method of writing(magnetization reversal) using a magnetic field generated by a current,and a method of writing (magnetization reversal) using a spin transfertorque (STT) generated by a current flowing in a stacking direction of amagnetoresistance effect element are known.

In magnetization reversal of a magnetoresistance effect element using anSTT, it is necessary for a current to flow in a stacking direction of amagnetoresistance effect element when data is written. A writing currentmay degrade characteristics of the magnetoresistance effect element.

Therefore, in recent years, attention has been focused on methods thatdo not require a current to flow in the stacking direction of amagnetoresistance effect element during writing. One method is a writingmethod using a spin-orbit torque (SOT) (for example, Non-Patent Document1). An SOT is induced by a pure spin current generated by spin-orbitinteraction or a Rashba effect at an interface between differentmaterials. A current for inducing an SOT in a magnetoresistance effectelement flows in a direction intersecting the stacking direction of themagnetoresistance effect element. A writing method using an SOT does notrequire a current to flow in the stacking direction of amagnetoresistance effect element, and a longer lifespan for amagnetoresistance effect element is expected to be able to be achievedtherewith.

CITATION LIST Non-Patent Literature Non-Patent Document 1

-   I. M. Miron, K. Garello, G. Gaudin, P.-J. Zermatten, M. V.    Costache, S. Auffret, S. Bandiera, B. Rodmacq, A. Schuhl, and P.    Gambardella, Nature, 476, 189 (2011).

SUMMARY OF INVENTION Technical Problem

When a current passes through a predetermined spin-orbit torque wiringcontaining heavy metals or the like, many spins are injected into aferromagnetic material, so that a large SOT is induced in theferromagnetic material. On the other hand, a spin-orbit torque wiring isinferior in thermal conductivity as compared to copper wiring, aluminumwiring, and the like that are generally used for wiring. When a currentis applied to a spin-orbit torque wiring, a temperature of aferromagnetic material connected to the spin-orbit torque wiringincreases, and thus a stability of magnetization of the ferromagneticmaterial decreases. The decrease of the stability of magnetization ofthe ferromagnetic material may cause a write error in amagnetoresistance effect element.

The present invention has been realized in view of the abovecircumstances, and provides a spin-orbit torque type magnetizationrotational element that has excellent heat exhaustion properties.

Solution to Problem

As a result of intensive studies, the present inventors have found aconfiguration of an element that has excellent heat exhaustionproperties. That is, the present invention provides the following meansin order to solve the above problems.

(1) A spin-orbit torque type magnetization rotational element accordingto a first aspect includes a spin-orbit torque wiring extending in afirst direction, a first ferromagnetic layer laminated in a seconddirection intersecting the spin-orbit torque wiring, and a firstnonmagnetic metal layer and a second nonmagnetic metal layer which areconnected to the spin-orbit torque wiring at positions sandwiching thefirst ferromagnetic layer in the first direction in a plan view seen inthe second direction, in which, in the first direction, a center ofgravity of the first ferromagnetic layer is positioned on either a firstnonmagnetic metal layer side or a second nonmagnetic metal layer sidefrom a reference point that is a center between the first nonmagneticmetal layer and the second nonmagnetic metal layer.

(2) The spin-orbit torque type magnetization rotational elementaccording to the above aspect may be configured such that the center ofgravity is positioned on the second nonmagnetic metal layer sidedeviating from the reference point, and the second nonmagnetic metallayer is positioned downstream when a current is applied to thespin-orbit torque wiring.

(3) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, a portion of the first ferromagneticlayer may overlap the reference point in a plan view seen in the seconddirection.

(4) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, the first nonmagnetic metal layer may bepositioned upstream when a current is applied to the spin-orbit torquewiring and has a first end portion on a first ferromagnetic layer side,and a distance D in the first direction between the first end portionand the center of gravity and a thickness T₂ of the spin-orbit torquewiring may satisfy the relationship of 6≤D/T₂≤56.

(5) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, widths of the first nonmagnetic metallayer and the second nonmagnetic metal layer may be wider than a widthof the first ferromagnetic layer.

(6) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, the thicknesses of the first nonmagneticmetal layer and the second nonmagnetic metal layer may be thicker thanthe thickness of the spin-orbit torque wiring, and widths of the firstnonmagnetic metal layer and the second nonmagnetic metal layer may bewider than a width of the spin-orbit torque wiring.

(7) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, the first nonmagnetic metal layer andthe second nonmagnetic metal layer may include any one of a groupconsisting of Ag, Au, Cu, Al, W, Co, Ni, Zn, Ta, TiN, and TaN.

(8) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, the first nonmagnetic metal layer andthe second nonmagnetic metal layer may be connected to a second surfaceon a side opposite to a first surface facing the first ferromagneticlayer of the spin-orbit torque wiring.

(9) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, the first nonmagnetic metal layer andthe second nonmagnetic metal layer may be connected to a first surfacefacing the first ferromagnetic layer of the spin-orbit torque wiring.

(10) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, the first nonmagnetic metal layer andthe second nonmagnetic metal layer may be connected to the spin-orbittorque wiring without an intervening oxide.

(11) In the spin-orbit torque type magnetization rotational elementaccording to the above aspects, a portion of the first ferromagneticlayer may overlap the first nonmagnetic metal layer or the secondnonmagnetic metal layer in a plan view seen in the second direction.

(12) The spin-orbit torque type magnetization rotational elementaccording to the above aspects may further include a control unit, whichallows a read current to flow between the first nonmagnetic metal layeror the second nonmagnetic metal layer overlapping the portion of thefirst ferromagnetic layer and the first ferromagnetic layer in a planview seen in the second direction.

(13) A spin-orbit torque magnetoresistance effect element according tothe second aspect includes a spin-orbit torque type magnetizationrotational element according to the above aspects, a nonmagnetic layerwhich is laminated on a fourth surface on a side opposite to the thirdsurface facing the spin-orbit torque wiring in the first ferromagneticlayer, and a second ferromagnetic layer sandwiching the nonmagneticlayer together with the first ferromagnetic layer.

(14) A magnetic memory according to a third aspect includes a pluralityof spin-orbit torque type magnetoresistance effect elements according tothe above aspects.

Advantageous Effects of Invention

It is possible to provide a spin-orbit torque type magnetic rotationalelement with excellent heat exhaustion properties.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of a spin-orbit torque typemagnetization rotational element according to a first embodiment.

FIG. 2 is a schematic plan view of the spin-orbit torque typemagnetization rotational element according to the first embodiment.

FIG. 3 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 4 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 5 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 6 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 7 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 8 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 9 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment.

FIG. 10 is a schematic cross-sectional view of a spin-orbit torque typemagnetoresistance effect element according to a second embodiment.

FIG. 11 is a schematic diagram of a magnetic memory according to a thirdembodiment including a plurality of spin-orbit torque magnetoresistanceeffect elements.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present embodiment will be described in detail withreference to the drawings as appropriate. In the drawings used in thefollowing description, in order to make features easier to understand,portions constituting the features may be shown in an enlarged mannerfor the sake of convenience, and dimensional proportions of therespective components may differ from actual ones. It should beunderstood that materials, dimensions, and the like exemplified in thefollowing description are merely examples, and the present invention isnot limited to these, and can be implemented with appropriatemodifications within a scope in which the effects of the presentinvention can be achieved.

First Embodiment

(Spin-Orbit Torque Type Magnetization Rotational Element)

FIG. 1 is a schematic cross-sectional view of a spin-orbit torque typemagnetization rotational element 10 according to the present embodiment,and FIG. 2 is a schematic plan view of the spin-orbit torque typemagnetization rotational element 10 according to the present embodiment.The spin-orbit torque type magnetization rotational element 10 includesa first ferromagnetic layer 1, a spin-orbit torque wiring 2, a firstnonmagnetic metal layer 3, and a second nonmagnetic metal layer 4. FIG.2 is a plan view seen in a z direction, and shows a surface of eachlayer on +z side.

Hereinafter, the present embodiment will be explained on the basis ofdefining a first direction in which the spin-orbit torque wiring 2extends as an x direction, a laminating direction (a second direction)of the first ferromagnetic layer 1 as the z direction, and a directionorthogonal to both the x direction and the z direction as a y direction.

<Spin-Orbit Torque Wiring>

The spin-orbit torque wiring 2 extends in the x direction. Thespin-orbit torque wiring 2 has a first surface 2A and a second surface2B. The first surface 2A faces a third surface 1A of the firstferromagnetic layer 1. Here, to “face” means a relationship of facingeach other, in which two layers may be in contact with each other or mayhave another layer therebetween. The spin-orbit torque wiring 2 in FIG.1 is directly connected to one surface of the first ferromagnetic layer1 in the z direction. The spin-orbit torque wiring 2 may be directlyconnected to the first ferromagnetic layer 1 or may be connected theretovia another layer.

The spin-orbit torque wiring 2 is made of a material that generates aspin current due to the spin Hall effect when a current I flows. As sucha material, any material that can generate a spin current in thespin-orbit torque wiring 2 is sufficient. Therefore, the material is notlimited to a material composed of a single element and may be configuredof a portion composed of a material that easily generates a spin currentand a portion composed of a material with which it is difficult togenerate a spin current.

The spin Hall effect is a phenomenon in which a spin current is inducedin a direction orthogonal to a direction of a current I on the basis ofa spin-orbit interaction when the current I flows through a wiring. Themechanism by which a spin current is generated by the spin Hall effectwill be described.

When a potential difference is applied to both ends of the spin-orbittorque wiring 2, the current I flows along the spin-orbit torque wiring2. When the current I flows, a first spin S1 oriented in one directionand a second spin S2 oriented in a direction opposite to the first spinS1 are respectively bent in directions orthogonal to the current. Forexample, the first spin S1 is bent in the z direction with respect to atraveling direction, and the second spin S2 is bent in the −z directionwith respect to the traveling direction.

The normal Hall effect and the spin Hall effect are the same in that amoving (traveling) charge (electrons) can bend the moving (traveling)direction. On the other hand, they are greatly different from each otherin that, in the normal Hall effect, charged particles moving in amagnetic field receive a Lorentz force and bend a direction of movement,whereas in the spin Hall effect, even in the absence of a magneticfield, traveling directions of the spins are bent only by movement ofelectrons (only a current flows).

In a nonmagnetic material (a material that is not a ferromagneticmaterial), the number of electrons of the first spin S1 is equal to thenumber of electrons of the second spin S2. Due to the spin Hall effect,the number of electrons of the first spin S1 directed in the +zdirection is equal to the number of electrons of the second spin S2directed in the −z direction in the figure. In this case, flows ofcharges cancel each other out, and thus an amount of current becomeszero. A spin current without an electric current is particularly calleda pure spin current.

When a flow of electrons of the first spin S1 is J_(↑), a flow ofelectrons of the second spin S2 is J_(↓), and a spin current is J_(S),the spin current is defined as J_(S)=J_(↑)−J_(↓). The spin current J_(S)flows in the z direction in the figure. In FIG. 1, there is the firstferromagnetic layer 1, which will be described later, on an uppersurface of the spin-orbit torque wiring 2. For this reason, the spin isinjected into the first ferromagnetic layer 1.

The spin-orbit torque wiring 2 is made of any one of a metal, an alloy,an intermetallic compound, a metal boride, a metal carbide, a metalsilicide, and a metal phosphide having a function of generating a spincurrent by the spin Hall effect when a current flows.

A main component of the spin-orbit torque wiring 2 is preferably anonmagnetic heavy metal. Here, the heavy metal means a metal having aspecific gravity equal to or higher than that of yttrium. A nonmagneticheavy metal is preferably a nonmagnetic metal having a large atomicnumber of 39 or more having d electrons or f electrons in the outermostshell. These nonmagnetic metals have a large spin-orbit interaction thatcauses the spin Hall effect.

Electrons generally move in a direction opposite to a current regardlessof their spin directions. On the other hand, nonmagnetic metals having alarge atomic number having d electrons or f electrons in the outermostshell have a large spin-orbit interaction and a strong spin Hall effect.For this reason, a direction in which electrons move depends ondirections of spins of electrons. Therefore, a spin current is easilyoccurs in these nonmagnetic heavy metals.

Also, the spin-orbit torque wiring 2 may include a magnetic metal. Themagnetic metal refers to a ferromagnetic metal or an antiferromagneticmetal. If a nonmagnetic metal contains a minute amount of a magneticmetal, it becomes a cause of spin scattering. When spins are scattered,the spin-orbit interaction is enhanced, and thus a generation efficiencyof the spin current with respect to the current is increased. A maincomponent of the spin-orbit torque wiring 2 may be composed only of anantiferromagnetic metal.

On the other hand, if an amount of the magnetic metal added is increasedtoo much, the generated spin current is scattered by the added magneticmetal, and as a result, an action of reducing the spin current maybecome stronger. Therefore, a molar ratio of the added magnetic metal ispreferably sufficiently smaller than a total of molar ratios of elementsconstituting the spin-orbit torque wiring. The molar ratio of themagnetic metal to be added is preferably 3% or less of the whole.

The spin-orbit torque wiring 2 may include a topological insulator. Atopological insulator is a substance in which the inside of thesubstance is an insulator or a high-resistance substance, but aspin-polarized metal state is generated on a surface thereof. Aninternal magnetic field due to a spin-orbit interaction is generated inthe substance. Therefore, even without an external magnetic field, a newtopological phase appears due to the effect of spin-orbit interaction.This is a topological insulator, and a pure spin current can begenerated with high efficiency due to a strong spin-orbit interactionand by breaking an inversion symmetry at an edge thereof.

As the topological insulator, for example, SnTe,Bi_(1.5)Sb_(0.5)Te_(1.7)Se_(1.3), TlBiSe₂, Bi₂Te₃, (Bi_(1-x)Sb_(x))₂Te₃,and the like are preferable. These topological insulators can generate aspin current with high efficiency.

<First Ferromagnetic Layer>

The first ferromagnetic layer 1 is laminated in the second direction (zdirection) intersecting the spin-orbit torque wiring 2. The firstferromagnetic layer 1 has the third surface 1A and a fourth surface 1B.The third surface 1A faces the first surface 2A of the spin-orbit torquewiring 2. The fourth surface 1B is a surface opposite to the thirdsurface 1A in the first ferromagnetic layer 1. The first ferromagneticlayer 1 functions by changing its magnetization direction. The firstferromagnetic layer 1 may be an in-plane magnetization film having adirection of easy magnetization in an x-y plane or a verticalmagnetization film having an axis of easy magnetization in the zdirection.

A ferromagnetic material, in particular, a soft magnetic material can beapplied to the first ferromagnetic layer 1. For example, a metalselected from the group consisting of Cr, Mn, Co, Fe, and Ni, an alloycontaining one or more of these metals, an alloy containing these metalsand at least one or more elements from B, C, and N can be used.Specifically, Co—Fe, Co—Fe—B, and Ni—Fe are exemplary examples.

Also, when the first ferromagnetic layer 1 is an in-plane magnetizationfilm, for example, a Co—Ho alloy (CoHo₂), an Sm—Fe alloy (SmFe₁₂), orthe like is preferably used.

The first ferromagnetic layer 1 may be a Heusler alloy. A Heusler alloyis a half metal and has a high spin polarizability. Heusler alloysinclude intermetallic compounds having a chemical composition of XYZ orX₂YZ. X is a transition metal element or a noble metal element of theCo, Fe, Ni, or Cu groups in the periodic table. Y is a transition metalof the Mn, V, Cr, or Ti groups, or the same types of element as for X. Zis a typical element of Group III to Group V. For example, Co₂FeSi,Co₂FeGe, Co₂FeGa, Co₂MnSi, Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b),Co₂FeGe_(1-c)Ga_(c), etc., are examples of Heusler alloys.

<First Nonmagnetic Metal Layer and Second Nonmagnetic Metal Layer>

The first nonmagnetic metal layer 3 and the second nonmagnetic metallayer 4 are desposed at positions sandwiching the first ferromagneticlayer 1 in a plan view seen in the z direction. By applying a potentialdifference between the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4, a current I flows in the spin-orbit torquewiring 2. The first nonmagnetic metal layer 3 and the second nonmagneticmetal layer 4 function as electrodes for flowing the current I throughthe spin-orbit torque wiring 2. The first nonmagnetic metal layer 3 iselectrically connected to, for example, an external power source. Thesecond nonmagnetic metal layer 4 is electrically connected to, forexample, an external reference potential. The current I flows on thebasis of a potential difference between the external power source andthe reference potential. For example, when the current I is applied tothe spin-orbit torque wiring 2, the first nonmagnetic metal layer 3 isat a position that becomes an upstream side (a side opposite to thereference potential) in a flowing direction of the current I. Forexample, when the current I is applied to the spin-orbit torque wiring2, the second nonmagnetic metal layer 4 is at a position that becomes adownstream side (a reference potential side) in the flowing direction ofthe current I. For example, when the second nonmagnetic metal layer 4 isconnected to the ground, the ground becomes the reference potential.

The first nonmagnetic metal layer 3 and the second nonmagnetic metallayer 4 preferably include any one of the group consisting of Ag, Au,Cu, Al, W, Co, Ni, Zn, Ta, TiN and TaN. These materials have anexcellent thermal conductivity and can efficiently exhaust heataccumulated in the spin-orbit torque wiring 2.

It is preferable that the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4 be directly connected to the spin-orbit torquewiring 2 without an intervening oxide that hinders heat conduction.

<Relationship Between Respective Components>

In the x direction, a center of gravity G of the first ferromagneticlayer 1 is positioned at a position deviating toward either the firstnonmagnetic metal layer 3 or the second nonmagnetic metal layer 4 from areference point S that is a center between the first nonmagnetic metallayer 3 and the second nonmagnetic metal layer 4. The reference point Sis a center of a line segment that connects a center of gravity of thefirst nonmagnetic metal layer 3 and a center of gravity of the secondnonmagnetic metal layer 4. When the first ferromagnetic layer 1, thefirst nonmagnetic metal layer 3, and the second nonmagnetic metal layer4 form a shape that is line-symmetric or point-symmetric in the xdirection in a plan view seen in the z direction, positions of theircenters and positions of their centers of gravity often coincide witheach other, respectively. For that reason, the positions of the centersof the first ferromagnetic layer 1, the first nonmagnetic metal layer 3,and the second nonmagnetic metal layer 4 in the x direction can berespectively regarded as the positions of the centers of gravity of thefirst ferromagnetic layer 1, the first nonmagnetic metal layer 3, andthe second nonmagnetic metal layer 4 in the x direction. That is, it canbe said in other words such that, in the x direction, the center of thefirst ferromagnetic layer 1 is positioned at a position deviating towardeither the first nonmagnetic metal layer 3 or the second nonmagneticmetal layer 4 from the reference point S that is the center between thefirst nonmagnetic metal layer 3 and the second nonmagnetic metal layer4.

Much of the heat accumulated in the spin-orbit torque wiring 2 isexhausted from the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4. For that reason, the reference point S of thespin-orbit torque wiring 2 has the highest temperature in the spin-orbittorque wiring 2, and the temperature decreases as going away from thereference point S in the x direction. When the position of the center ofgravity G of the first ferromagnetic layer 1 and the reference point Sin the x direction overlap, magnetization of the first ferromagneticlayer 1 is easily affected by heat, and thus an unintended magnetizationreversal due to the heat easily occurs.

On the other hand, if the positions of the center of gravity G of thefirst ferromagnetic layer 1 and the reference point S in the x directiondeviate from each other, the center of gravity G of the firstferromagnetic layer 1 can be shifted from the highest temperatureposition. That is, it is possible to prevent the magnetization of thefirst ferromagnetic layer 1 from causing an unintended magnetizationreversal due to heat.

The center of gravity G of the first ferromagnetic layer 1 is preferablyseparated from the reference point S by 15% or more of the distancebetween the first nonmagnetic metal layer 3 and the second nonmagneticmetal layer 4, and more preferably separated from the reference point Sby 25% or more. The distance between the first nonmagnetic metal layer 3and the second nonmagnetic metal layer 4 is a length of theperpendicular to an imaginary line extending in the y direction from thecenter of gravity of the first nonmagnetic metal layer 3 through thecenter of gravity of the second nonmagnetic metal layer 4. The center ofgravity G of the first ferromagnetic layer 1 is preferably separatedaway from the reference point S by 15 nm or more, and more preferablyseparated by 25 nm or more.

Although the center of gravity G of the first ferromagnetic layer 1 maybe positioned on the first nonmagnetic metal layer 3 side or on thesecond nonmagnetic metal layer 4 side while deviating from the referencepoint S, it is preferably positioned on the second nonmagnetic metallayer 4 side, which is positioned downstream in the flowing direction ofthe current I, as shown in FIG. 1.

The current I flows from the first nonmagnetic metal layer 3 to thespin-orbit torque wiring 2. The vicinity of an interface betweendifferent substances is easily affected by a contact resistance and thelike. That is, a flow of the current I tends to be unstable in thevicinity of the interface between the first nonmagnetic metal layer 3and the spin-orbit torque wiring 2. When the center of gravity G of thefirst ferromagnetic layer 1 is positioned downstream in the flowingdirection of the current I, the current I that flows in the spin-orbittorque wiring 2 is stabilized when it reaches the first ferromagneticlayer 1. When the current I is stabilized, an amount of spin injectedinto the first ferromagnetic layer 1 is stabilized by the spin Halleffect, and a magnetization reversal of the first ferromagnetic layer 1is stabilized.

Further, the distance D in the x direction between a first end portion 3a of the first nonmagnetic metal layer 3 on the first ferromagneticlayer 1 side and the center of gravity G and the thickness T₂ of thespin-orbit torque wiring 2 preferably satisfy the relationship of6≤D/T₂≤56, and more preferably satisfy the relationship of 10≤D/T₂≤34.Here, the first end portion 3 a is an end portion on the firstferromagnetic layer 1 side of a contact surface between the spin-orbittorque wiring 2 and the first nonmagnetic metal layer 3 in a crosssection passing through a center of the spin-orbit torque wiring 2 in awidth direction (y direction). The thickness T₂ of the spin-orbit torquewiring 2 is an average thickness of the spin-orbit torque wiring 2.

When the thickness T₂ of the spin-orbit torque wiring 2 varies, acurrent density of the current I changes. If the current density of thecurrent I varies, a distance required until the current I stabilizeschanges. By satisfying the above relational equations, it is possible tostabilize the amount of spin injected into the first ferromagnetic layer1 due to the spin Hall effect.

A distance d in the x direction between the first end portion 3 a and anend portion 1 a of the first ferromagnetic layer 1 on the firstnonmagnetic metal layer 3 side and the thickness T₂ of the spin-orbittorque wiring 2 preferably satisfy the relationship of 3≤d/T₂≤23, andmore preferably satisfy the relationship of 5≤d/T₂≤15. The end portion 1a is an end portion positioned closest to the first nonmagnetic metallayer 3 in the first ferromagnetic layer 1 in a cross section passingthrough the center of the spin-orbit torque wiring 2 in the widthdirection (y direction). When the first end portion 3 a and the endportion 1 a satisfy the above relationship, the current I is stabilizedwhen it reaches the first ferromagnetic layer 1.

The thickness T₂ of the spin-orbit torque wiring 2 is, for example,preferably 1 nm or more and 15 nm or less, more preferably 2 nm or moreand 10 nm or less, and further preferably 3 nm or more and 5 nm or less.

The distance D between the first end portion 3 a and the center ofgravity G is, for example, preferably 10 nm or more and 150 nm or less,more preferably 15 nm or more and 100 nm or less, and further preferably20 nm or more and 75 nm or less.

The distance d between the first end portion 3 a and the end portion 1 ais, for example, preferably 15 nm or more and 100 nm or less, morepreferably 20 nm or more and 75 nm or less, and further preferably 25 nmor more and 50 nm or less.

As shown in FIGS. 1 and 2, it is preferable that a portion of the firstferromagnetic layer 1 overlap the reference point S in a plan view seenin the z direction. In the present specification, “in a plan view seenin the z direction” refers to the widest region occupied by each layerwhen viewed in the z direction. When an area of the third surface 1A ofthe first ferromagnetic layer 1 is larger than an area of the fourthsurface 1B of the first ferromagnetic layer 1 (For example, a crosssection of the first ferromagnetic layer 1 is a trapezoid having a topbottom in the +z direction), the third surface 1A becomes a referencefor overlapping the reference point S. The reference point S and thefirst ferromagnetic layer 1 partially overlap in a plan view seen in thez direction in a state where the center of gravity G of the firstferromagnetic layer 1 is at a position deviating from the referencepoint S, a volume of the first ferromagnetic layer 1 increases. As thevolume of the first ferromagnetic layer 1 increases, a magnetic strengthof the entire first ferromagnetic layer 1 increases, and thus thestability of magnetization increases. Further, when data is written,heat generated in the spin-orbit torque wiring 2 can be used formagnetization reversal, and the magnetization reversal can befacilitated.

Here, it is also thought that the use of the heat generated in thespin-orbit torque wiring 2 for the magnetization reversal may lead to anerroneous writing due to the heat generated in the spin-orbit torquewiring 2. However, the positions of the reference point S generating themost heat and the center of gravity G deviate from each other, and themagnetic strength of the entire first ferromagnetic layer 1 is high, aninfluence of heat on the magnetization of the first ferromagnetic layer1 is sufficiently inhibited. For that reason, heat cannot give the firstferromagnetic layer 1 enough energy for reaching an erroneous writing,but rather becomes a factor assisting the magnetization reversal.

The first ferromagnetic layer 1 preferably occupies 7% or more of anarea of the spin-orbit torque wiring 2 in a plan view seen in the zdirection, more preferably occupies 15% or more, further preferablyoccupies 30% or more, and yet further preferably occupies 50% or more.As described above, when the volume of the first ferromagnetic layer 1increases, the magnetic strength of the entire first ferromagnetic layer1 increases and thus the stability of magnetization is enhanced.

As shown in FIG. 1, a thickness T₃ of the first nonmagnetic metal layer3 and a thickness T₄ of the second nonmagnetic metal layer 4 arepreferably thicker than the thickness T₂ of the spin-orbit torque wiring2, and preferably thicker twice or more the thickness T₂ of thespin-orbit torque wiring 2. Also, as shown in FIG. 2, a width W₃ of thefirst nonmagnetic metal layer 3 and a width W₄ of the second nonmagneticmetal layer 4 are preferably wider than a width W₂ of the spin-orbittorque wiring 2, and preferably wider twice or more the width W₂ of thespin-orbit torque wiring 2. By satisfying these relationships, heatcapacities of the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4 increase, and thus the amount of heatgenerated in the spin-orbit torque wiring 2 can be sufficientlyexhausted. The thickness of each layer is an average thickness of eachlayer. The widths of the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4 are the maximum values of the widths of thefirst nonmagnetic metal layer 3 and the second nonmagnetic metal layer 4in the y direction on the first surfaces 3A and 4A of the firstnonmagnetic metal layer 3 and the second nonmagnetic metal layer 4 onthe spin-orbit torque wiring 2 side. The width of the spin-orbit torquewiring 2 is an average value of a width of the second surface 2B of thespin-orbit torque wiring 2 in the y direction at a position overlappingthe first nonmagnetic metal layer 3 or the second nonmagnetic metallayer 4 in a plan view seen in the z direction.

The thickness T₃ of the first nonmagnetic metal layer 3 and thethickness T₄ of the second nonmagnetic metal layer 4 are preferably 10nm or more and 100 nm or less, more preferably 15 nm or more and 75 nmor less, and further preferably 20 nm or more and 50 nm or less.

The width W₃ of the first nonmagnetic metal layer 3 and the width W₄ ofthe second nonmagnetic metal layer 4 are preferably 80 nm or more and600 nm or less, more preferably 100 nm or more and 500 nm or less, andfurther preferably 120 nm or more and 400 nm or less.

Further, the width W₂ of the spin-orbit torque wiring 2 is preferably 40nm or more and 300 nm or less, more preferably 50 nm or more and 250 nmor less, and further preferably 60 nm or more and 200 nm or less.

There are heat conduction, advection (convection), and heat radiation ina process of carrying heat. Although the present invention has mainlybeen explained on the basis of heat conduction as described above,considering effects of heat radiation, the widths W₃ and W₄ of the firstnonmagnetic metal layer 3 and the second nonmagnetic metal layer 4 arepreferably wider than the width Wi of the first ferromagnetic layer.When the spin-orbit torque wiring 2 generates heat, the firstferromagnetic layer 1 also generates heat. If the heat accumulated inthe first ferromagnetic layer 1 is immediately radiated, an unintendedmagnetization reversal of the first ferromagnetic layer 1 due to heatcan be prevented.

The heat accumulated in the first ferromagnetic layer 1 isotropicallydiffuses around the first ferromagnetic layer 1 due to heat radiation.When the widths W₃ and W₄ of the first nonmagnetic metal layer 3 and thesecond nonmagnetic metal layer 4 are wider than the width Wi of thefirst ferromagnetic layer 1, the first nonmagnetic metal layer 3 and thesecond nonmagnetic metal layer 4 can receive much of the heat spreadingfrom the first ferromagnetic layer 1. The heat received by the firstnonmagnetic metal layer 3 and the second nonmagnetic metal layer 4 isquickly exhausted by the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4 which have excellent thermal conductivity. Asa result, the heat radiation from the first ferromagnetic layer 1proceeds promptly, and thus an unintended magnetization reversal of thefirst ferromagnetic layer 1 due to heat can be prevented. The width ofthe first ferromagnetic layer 1 is a width of the third surface 1A inthe y direction at the center of the first ferromagnetic layer 1 in thex direction.

The width Wi of the first ferromagnetic layer 1 is preferably 10 nm ormore and 200 nm or less, more preferably 20 nm or more and 100 nm orless, and further preferably 25 nm or more and 80 nm or less.

The width W₁ of the first ferromagnetic layer 1 is preferably narrowerthan the width W₂ of the spin-orbit torque wiring 2. The spin thatcauses SOT is supplied from the spin-orbit torque wiring 2. Bysatisfying this relationship, an in-plane magnetic variation of thefirst ferromagnetic layer 1 can be inhibited.

In the spin-orbit torque type magnetization rotational element 10 shownin FIG. 1, the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4 are connected to the second surface 2B on aside opposite to the first surface 2A facing the first ferromagneticlayer 1 of the spin-orbit torque wiring 2. In the case of the aboveconfiguration, wirings connected to the first nonmagnetic metal layer 3and the second nonmagnetic metal layer 4 can be easily routed, and thusthe spin-orbit torque type magnetization rotational element 10 can beeasily manufactured.

On the other hand, like the spin-orbit torque type magnetizationrotational element 11 shown in FIG. 3, the first nonmagnetic metal layer3 and the second nonmagnetic metal layer 4 may be connected to the firstsurface facing the first ferromagnetic layer 1 of the spin-orbit torquewiring 2. In the case that the first nonmagnetic metal layer 3 and thesecond nonmagnetic metal layer 4 are connected to the same plane as thefirst ferromagnetic layer 1, distances between the first nonmagneticmetal layer 3 or the second nonmagnetic metal layer 4 and the firstferromagnetic layer 1 become closer. For that reason, heat from thefirst ferromagnetic layer 1 is quickly exhausted due to heat radiation,and thus an unintended magnetization reversal of the first ferromagneticlayer 1 due to heat can be prevented.

In this case, the thicknesses T₃ and T₄ of the first nonmagnetic metallayer 3 and the second nonmagnetic metal layer 4 are preferably thickerthan the thickness T₁ of the first ferromagnetic layer. The thickness Tiof the first ferromagnetic layer 1 is preferably 0.5 nm or more and 3.0nm or less, more preferably 0.7 nm or more and 2.5 nm or less, andfurther preferably 0.9 nm or more and 2.0 nm or less.

As described above, according to the spin-orbit torque typemagnetization rotational elements 10 and 11 according to the presentembodiment, an influence of the heat generated by the spin-orbit torquewiring 2 on the first ferromagnetic layer 1 can be reduced. That is, itcan be inhibited that a temperature of the first ferromagnetic layer 1increases thereby lowering a stability of magnetization of the firstferromagnetic layer. The spin-orbit torque type magnetization rotationalelements 10 and 11 can be used alone as an anisotropic magnetic sensorand an optical element utilizing a magnetic Kerr effect or a magneticFaraday effect.

Although an example of the first embodiment has been described in detailabove, the first embodiment is not limited to this example, and variousmodifications and changes can be made within the scope of the gist ofthe present invention described in the claims.

FIG. 4 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment. The same components as those in FIG. 1 are denoted bythe same reference signs, and the description thereof will be omitted.

A portion of the first ferromagnetic layer 1 shown in FIG. 4 overlapsthe second nonmagnetic metal layer 4 in a plan view seen in the zdirection. The first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4 have excellent thermal conductivity, andefficiently remove heat from the first ferromagnetic layer 1. Bydisposing a portion of the first ferromagnetic layer 1 closer to thesecond nonmagnetic metal layer 4, a stability of magnetization of thefirst ferromagnetic layer 1 increases.

Further, the spin-orbit torque type magnetization rotational element 12shown in FIG. 4 has a control unit 7 for flowing a read current. Thecontrol unit 7 includes, for example, a first transistor 7A and a secondtransistor 7B. When the first transistor 7A and the second transistor 7Bare turned on, a read current flows in the order of the firstferromagnetic layer 1, the spin-orbit torque wiring 2, and the secondnonmagnetic metal layer 4.

A read resistance value is a resistance value between the firstferromagnetic layer 1 and the second nonmagnetic metal layer 4. Morespecifically, the read resistance value is obtained by adding inherentresistance values of portions through which the read current flows ineach of the first ferromagnetic layer 1, the spin-orbit torque wiring 2,and the second nonmagnetic metal layer 4 and an anisotropicmagnetoresistance effect of the first ferromagnetic layer 1. In the caseof a spin-orbit torque type magnetoresistance effect element which willbe described later, a resistance value obtained by adding an inherentresistance value of each layer and a resistance value resulting from adifference in relative angle between the magnetization of the firstferromagnetic layer 1 and the magnetization of the second ferromagneticlayer 6 becomes the read resistance value. When a distance where theread current flows along the spin-orbit torque wiring 2 becomes longer,a portion where the read current flows in the spin-orbit torque wiring 2becomes larger, and thus the inherent resistance value of the portionbecomes larger. When the read resistance value increases, it becomesdifficult to read an amount of change in resistance value. On the otherhand, when a portion of the first ferromagnetic layer 1 overlaps thesecond nonmagnetic metal layer 4 and a flowing direction of the readcurrent is controlled, a change in resistance value can be read outsensitively.

Although FIG. 4 shows an example in which the first ferromagnetic layer1 and the second nonmagnetic metal layer 4 overlap each other, the firstferromagnetic layer 1 and the first nonmagnetic metal layer 3 mayoverlap each other.

FIGS. 5 and 6 are schematic cross-sectional views of another example ofthe spin-orbit torque type magnetization rotational element according tothe first embodiment. The same components as those in FIG. 1 are denotedby the same reference signs and the description thereof will be omitted.Also, in FIG. 5 and FIG. 6, an insulating layer 30 surrounding the firstnonmagnetic metal layer 3 and the second nonmagnetic metal layer 4 andan electrode 9 connected to the first ferromagnetic layer 1 are shown atthe same time. The insulating layer 30 is an interlayer insulating film,and is, for example, SiO₂ or SiN. The electrode 9 is made of a materialhaving excellent conductivity, and is, for example, Cu. The center ofgravity G of the first ferromagnetic layer 1 and the reference point Sare at different positions in the x direction.

First surfaces 3A′ and 4A′ of the first nonmagnetic metal layer 3 andthe second nonmagnetic metal layer 4 shown in FIGS. 5 and 6 are recessedwith respect to a first surface 30A of the insulating layer 30. Sincethe insulating layer 30, the first nonmagnetic metal layer 3 and thesecond nonmagnetic metal layer 4 have different etching rates, the firstsurfaces 3A′ and 4A′ may be curved.

The spin-orbit torque wiring 2 is laminated on the first surfaces 30A,3A′, and 4A′. The spin-orbit torque wiring 2 has a first surface 2A′, asecond surface 2B′, a first side surface 2Sa, and a second side surface2Sb. The first side surface 2Sa and the second side surface 2Sb areinclined with respect to the z direction, for example. The first surface2A′ and the second surface 2B′ of the spin-orbit torque wiring 2 reflectshapes of the first surfaces 30A, 3A′, and 4A′. The spin-orbit torquewiring 2 has a portion that extends substantially parallel to the x-yplane along the first surface 30A, and a portion that curves withrespect to the x-y plane along the first surfaces 3A′ and 4A′.

The first ferromagnetic layer 1 is laminated on the first surface 2A′ ofthe spin-orbit torque wiring 2. The third surface 1A′ and the fourthsurface 1B′ of the first ferromagnetic layer 1 reflect a shape of thefirst surface 2A′ of the spin-orbit torque wiring 2.

The first ferromagnetic layer 1 has a first region R1 and a secondregion R2. The first region R1 is a portion that extends substantiallyparallel to the x-y plane. The second region R2 is a portion inclinedwith respect to the x-y plane. The first ferromagnetic layer 1 has athird surface 1A′, a fourth surface 1B′, a first side surface 1Sa, and asecond side surface 1Sb. The first side surface 1Sa and the second sidesurface 1Sb are inclined with respect to the z direction, for example.The first side surface 1Sa and the second side surface 1Sb are atdifferent positions in the x direction from the first side surface 2Saand the second side surface 2Sb of the spin-orbit torque wiring 2. Forthat reason, the first side surface 1Sa and the first side surface 2Saare discontinuous with each other, and the second side surface 1Sb andthe second side surface 2Sb are discontinuous with each other.

The third surface 1A′ has a first portion 1A′a and a second portion1A′b. The first portion 1A′a is the third surface 1A′ in the firstregion R1. The second portion 1A′b is the third surface 1A′ in thesecond region R2. The fourth surface 1B′ has a first portion 1B′a and asecond portion 1B′b. The first portion 1B′a is the fourth surface 1B′ inthe first region R1. The second portion 1B′b is the fourth surface 1B′in the second region R2. The first portions 1A′a and 1B′a are flat, andthe magnetization is oriented in a predetermined direction. The secondportions 1A′b and 1B′b are inclined with respect to the first portions1A′a and 1B′a, and the magnetization is inclined from a predetermineddirection. The magnetization of the second region R2 is easier to rotatethan that of the first region R1.

In the spin-orbit torque type magnetization rotational element 13 shownin FIG. 5, the position of the center of gravity G of the firstferromagnetic layer 1 in the x direction and the position of the secondnonmagnetic metal layer 4 in the x direction do not overlap each other,and the first region R1 is wider than the second region R2. In thespin-orbit torque type magnetization rotational element 13, the firstregion R1 ensures stability of magnetization, and the second region R2facilitates magnetization reversal.

The spin-orbit torque type magnetization rotational element 14 shown inFIG. 6 is different from the spin-orbit torque type magnetizationrotational element 13 shown in FIG. 5 in that the position of the centerof gravity G of the first ferromagnetic layer 1 in the x directionoverlaps the position of the second nonmagnetic metal layer 4 in the xdirection. The same components as those in FIG. 5 are denoted by thesame reference signs, and the description thereof will be omitted. Thefirst side surface 1Sa of the first ferromagnetic layer 1 and the firstside surface 2Sa of the spin-orbit torque type magnetization rotationalelement 2 are continuous with each other. The term “continuous” meansthat an inclined surface does not have an inflection point that changesdiscontinuously. For example, in the XZ plane, the first side surfaces1Sa and 2Sa can be regarded as continuously changing when an asymptoticline can be drawn with continuous straight lines or curves. The firstregion R1 is narrower than the second region R2. In the spin-orbittorque type magnetization rotational element 14, the magnetizationreversal of the first ferromagnetic layer 1 becomes easier.

FIG. 7 is a schematic cross-sectional view of another example of thespin-orbit torque type magnetization rotational element according to thefirst embodiment. The spin-orbit torque type magnetization rotationalelement 15 shown in FIG. 7 is different from the spin-orbit torque typemagnetization rotational element 13 shown in FIG. 5 in that the firstsurface 2A of the spin-orbit torque wiring 2, the third surface 1A andthe fourth surface 1B of the first ferromagnetic layer 1 are flat. Thesame components as those in FIG. 5 are denoted by the same referencesigns, and the description thereof will be omitted. In FIG. 7, theinsulating layer 30 and the electrode 9 are shown at the same time.

When the first surface 2A′ of the spin-orbit torque type magnetizationrotational element 13 shown in FIG. 5 is polished by chemical mechanicalpolishing (CMP) or the like, the spin-orbit torque type magnetizationrotational element 15 shown in FIG. 7 is obtained. When the firstsurface 2A is flattened, stability of magnetization of the firstferromagnetic layer 1 increases. The spin-orbit torque wiring 2 has afirst region R1′ and a second region R2′. The first region RI′ is aportion overlapping the first nonmagnetic metal layer 3 or the secondnonmagnetic metal layer 4 in a plan view seen in the z direction. Thesecond region R2′ is another region. The first region R1′ is thinnerthan the second region R2′. The first region R1′ is a portion thattransfers heat to the first nonmagnetic metal layer 3 or the secondnonmagnetic metal layer 4. When the thickness of the first region R1′ isthick, heat dissipation is improved. The second region R2′ is a portionthat supplies spin to the first ferromagnetic layer 1. If the thicknessof the second region R2′ is thin, the current density of the currentflowing through the second region R2′ can be increased, and thus themagnetization reversal can be performed efficiently.

Although an example in which the first surfaces 3A′ and 4A′ of the firstnonmagnetic metal layer 3 and the second nonmagnetic metal layer 4 arerecessed with respect to the first surface 30A of the insulating layer30 has been described in FIGS. 5, 6, and 7, the first surfaces 3A′ and4A′ of the first nonmagnetic metal layer 3 and the second nonmagneticmetal layer 4 may protrude from the first surface 30A of the insulatinglayer 30.

Also, FIGS. 8 and 9 are schematic cross-sectional views of anotherexample of the spin-orbit torque type magnetization rotational elementaccording to the first embodiment. The same components as those in FIG.1 are denoted by the same reference signs, and the description thereofwill be omitted. In addition, in FIGS. 8 and 9, the insulating layer 30and the electrode 9 are shown at the same time.

The spin-orbit torque wiring 2 of the spin-orbit torque typemagnetization rotational element 16 shown in FIG. 8 extends outward inthe x direction from the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4. The spin-orbit torque wiring 2 is processedinto a line after the layers are laminated. By extending the spin-orbittorque wiring 2 in the x direction, a processing margin can be secured.

The spin-orbit torque wiring 2 of the spin-orbit torque typemagnetization rotational element 17 shown in FIG. 9 is positioned insidethe first nonmagnetic metal layer 3 and the second nonmagnetic metallayer 4 in the x direction. Some portions of the first nonmagnetic metallayer 3 and the second nonmagnetic metal layer 4 are cut away byprocessing. The first surface 3A of the first nonmagnetic metal layer 3has a first portion 3A1 and a second portion 3A2. The first portion 3A1is a portion substantially parallel to the x-y plane. The second portion3A2 is a portion that inclines discontinuously with respect to the firstportion 3A1. The first surface 4A of the second nonmagnetic metal layer4 has a first portion 4A1 and a second portion 4A2. The first portion4A1 is a portion substantially parallel to the x-y plane. The secondportion 4A2 is a portion that inclines discontinuously with respect tothe first portion 4A1. The first side surface 2Sa of the spin-orbittorque wiring 2 is continuous with the second portion 4A2 of the secondnonmagnetic metal layer 4. The second side surface 2Sb of the spin-orbittorque wiring 2 is continuous with the second portion 3A2 of the firstnonmagnetic metal layer 3.

The spin-orbit torque type magnetization rotational element 17 is oftenused by integrating a plurality of elements. For example, the firstnonmagnetic metal layer 3 or the second nonmagnetic metal layer 4 of thedifferent spin-orbit torque type magnetization rotational element 17 maybe adjacent to the second nonmagnetic metal layer 4 side. By cutting outsome portions of the first nonmagnetic metal layer 3 and the secondnonmagnetic metal layer 4, the influence of the electric field generatedaround the first nonmagnetic metal layer 3 and the second nonmagneticmetal layer 4 can be reduced. As a result, the distance between adjacentspin-orbit torque type magnetization rotational elements 17 can bereduced, and thus a degree of integration of the spin-orbit torque typemagnetization rotational elements 17 can be increased.

Also, the respective modifications shown in FIGS. 4 to 9 can be combinedwith each other. For example, in the modification shown in FIGS. 4 to 7,the first side surface 2Sa of the spin-orbit torque wiring 2 may bepositioned outside the first nonmagnetic metal layer 3 or positionedinside it. The same applies to the second side surface 2Sb and thesecond nonmagnetic metal layer 4.

Second Embodiment

(Spin-Orbit Torque Type Magnetoresistance Effect Element)

FIG. 10 is a schematic cross-sectional view of a spin-orbit torque typemagnetoresistance effect element 20 according to a second embodiment.The spin-orbit torque type magnetoresistance effect element 20 shown inFIG. 10 includes a first ferromagnetic layer 1, a spin-orbit torquewiring 2, a first nonmagnetic metal layer 3, a second nonmagnetic metallayer 4, a nonmagnetic layer 5, and a second ferromagnetic layer 6. Thefirst ferromagnetic layer 1, the spin-orbit torque wiring 2, the firstnonmagnetic metal layer 3 and the second nonmagnetic metal layer 4correspond to those in the spin-orbit torque type magnetizationrotational element 10 according to the first embodiment shown in FIG. 1.Descriptions of constituents equivalent to those of the spin-orbittorque type magnetization rotational element 10 of the first embodimentwill be omitted.

A laminate (a functional unit 8) in which the first ferromagnetic layer1, the nonmagnetic layer 5, and the second ferromagnetic layer 6 arelaminated functions in the same manner as a normal magnetoresistanceeffect element. The functional unit 8 functions when the magnetizationof the second ferromagnetic layer 6 is fixed in one direction (zdirection) and the magnetization direction of the first ferromagneticlayer 1 changes relatively. In the case of being applied to a coerciveforce difference type (a pseudo spin valve type) MRAM, a coercive forceof the second ferromagnetic layer 6 is made larger than a coercive forceof the first ferromagnetic layer 1. In the case of being applied to anexchange bias type (spin valve type) MRAM, the magnetization of thesecond ferromagnetic layer is fixed by exchange coupling with anantiferromagnetic layer.

In the case in which the nonmagnetic layer 5 is made of an insulator,the functional unit 8 has the same configuration as that of a tunnelingmagnetoresistance (TMR) effect element, and in the case of being made ofmetal, it has the same configuration as that of a giantmagnetoresistance (GMR) effect element.

The laminated structure of the functional unit 8 can employ a laminatedstructure of known magnetoresistance effect elements. For example, eachlayer may be configured of a plurality of layers, or may be providedwith other layers such as an antiferromagnetic layer for fixing amagnetization direction of the second ferromagnetic layer 6. The secondferromagnetic layer 6 is called a fixed layer or a reference layer, andthe first ferromagnetic layer 1 is called a free layer or a storagelayer.

As the material of the second ferromagnetic layer 6, the same materialas that of the first ferromagnetic layer 1 can be used. In order tofurther increase the coercive force of the second ferromagnetic layer 6with respect to the first ferromagnetic layer 1, an antiferromagneticmaterial such as IrMn or PtMn may be used as a material in contact withthe second ferromagnetic layer 6. Further, in order to prevent a leakageof a magnetic field of the second ferromagnetic layer 6 from affectingthe first ferromagnetic layer 1, a synthetic ferromagnetic couplingstructure may be used.

A known material can be used for the nonmagnetic layer 5.

For example, in the case in which the nonmagnetic layer 5 is made of aninsulator (when it is a tunnel barrier layer), Al₂O₃, SiO₂, MgO,MgAl₂O₄, or the like can be used as the material thereof. In addition tothese, a material in which a part of Al, Si, Mg is substituted with Zn,Be, or the like can also be used as the nonmagnetic layer 5. Among theabove, MgO and MgAl₂O₄ are materials that can realize a coherent tunnel.In the case in which the nonmagnetic layer 5 is made of a metal, Cu, Au,Ag, or the like can be used as the material thereof. Further, in thecase in which the nonmagnetic layer 5 is made of a semiconductor, Si,Ge, CuInSe₂, CuGaSe₂, Cu(In, Ga)Se₂, or the like can be used as thematerial thereof.

The functional unit 8 may have other layers. An underlayer may beprovided on the surface of the first ferromagnetic layer 1 opposite tothe nonmagnetic layer 5. It is preferable that the layer disposedbetween the spin-orbit torque wiring 2 and the first ferromagnetic layer1 not dissipate the spin propagating from the spin-orbit torque wiring2.

For example, it is known that silver, copper, magnesium, aluminum, andthe like have a long spin diffusion length of 100 nm or more and aredifficult to dissipate spin. The thickness of this layer is preferablyless than or equal to a spin diffusion length of the materialconstituting the layer. If the thickness of the layer is less than orequal to the spin diffusion length, the spin propagating from thespin-orbit torque wiring 2 can be sufficiently transmitted to the firstferromagnetic layer 1.

Also in the spin-orbit torque type magnetoresistance effect elementaccording to the second embodiment, the position of the center G of thefirst ferromagnetic layer 1 and the reference point S in the x directiondeviate from each other. Therefore, the influence of the heat generatedby the spin-orbit torque wiring 2 on the first ferromagnetic layer 1 isreduced, and thus the stability of magnetization of the firstferromagnetic layer 1 increases. That is, the spin-orbit torque typemagnetoresistance effect element according to the second embodiment hasa low writing error rate.

Third Embodiment

(Magnetic Memory)

FIG. 11 is a schematic diagram of a magnetic memory 100 including aplurality of spin-orbit torque type magnetoresistance effect elements 20(see FIG. 10). FIG. 10 corresponds to a cross-sectional view of thespin-orbit torque type magnetoresistance effect element 20 taken alongplane A-A of FIG. 11. In the magnetic memory 100 shown in FIG. 11, thespin-orbit torque type magnetoresistance effect elements 20 are arrangedin a 3×3 matrix. FIG. 11 shows an example of a magnetic memory, and thenumber and arrangement of the spin-orbit torque type magnetoresistanceeffect elements 20 are arbitrary.

The spin-orbit torque type magnetoresistance effect elements 20 areconnected to one word line WL1 to WL3, one bit line BL1 to BL3, and oneread line RL1 to RL3, respectively.

By selecting the word lines WL1 to WL3 and bit lines BL1 to BL3 to whichcurrent is applied, the current passes through the spin-orbit torquewiring 2 of the arbitrary spin-orbit torque type magnetoresistanceeffect element 20 to perform a writing operation. Further, by selectingthe read lines RL1 to RL3 and the bit lines BL1 to BL3 to which currentis applied, the current passes in the laminating direction of thefunctional unit 8 of the arbitrary spin-orbit torque typemagnetoresistance effect element 20 to perform a reading operation. Theword lines WL1 to WL3, the bit lines BL1 to BL3, and the read lines RL1to RL3 to which current is applied can be selected by transistors or thelike. In other words, the data of an arbitrary element can be read fromthe plurality of spin-orbit torque type magnetoresistance effectelements 20 to be used as a magnetic memory.

Although the preferred embodiments of the present invention have beendescribed in detail above, it should be understood that the presentinvention is not limited to specific embodiments, and variousmodifications and changes are possible within the scope of the gist ofthe present invention described in the claims.

REFERENCE SIGNS LIST

-   -   1 First ferromagnetic layer    -   1 a End portion    -   1A, 2A, 3A, 4A, 1A′, 2A′, 3A′, 4A′ Third surface    -   1B, 2B, 1B′, 2B′ Fourth surface    -   2 Spin-orbit torque wiring    -   3 First nonmagnetic metal layer    -   3 a First end portion    -   4 Second nonmagnetic metal layer    -   5 Nonmagnetic layer    -   6 Second ferromagnetic layer    -   8 Functional unit    -   10 Spin-orbit torque type magnetization rotational element    -   20 Spin-orbit torque type magnetoresistance effect element    -   100 Magnetic memory    -   G Center of gravity    -   S Reference point

What is claimed is:
 1. A spin-orbit torque type magnetization rotationalelement comprising: a spin-orbit torque wiring extending in a firstdirection; a first ferromagnetic layer laminated with the spin-orbittorque wiring in a second direction intersecting the first direction;and a first nonmagnetic metal layer and a second nonmagnetic metal layerwhich are connected to the spin-orbit torque wiring at positionssandwiching the first ferromagnetic layer in the first direction in aplan view seen in the second direction, wherein, in the first direction,a center of gravity of the first ferromagnetic layer is positioned at aposition deviating toward either a first nonmagnetic metal layer side ora second nonmagnetic metal layer side from a reference point that is acenter between the first nonmagnetic metal layer and the secondnonmagnetic metal layer.
 2. The spin-orbit torque type magnetizationrotational element according to claim 1, wherein the center of gravityis positioned at a position deviating toward the second nonmagneticmetal layer side from the reference point, and the second nonmagneticmetal layer is positioned downstream when a current is applied to thespin-orbit torque wiring.
 3. The spin-orbit torque type magnetizationrotational element according to claim 1, wherein a portion of the firstferromagnetic layer overlaps the reference point in a plan view seen inthe second direction.
 4. The spin-orbit torque type magnetizationrotational element according to claim 1, wherein the first nonmagneticmetal layer is positioned upstream when a current is applied to thespin-orbit torque wiring and has a first end portion on a firstferromagnetic layer side, and a distance D in the first directionbetween the first end portion and the center of gravity and a thicknessT₂ of the spin-orbit torque wiring satisfy the relationship of6≤D/T₂≤56.
 5. The spin-orbit torque type magnetization rotationalelement according to claim 1, wherein widths of the first nonmagneticmetal layer and the second nonmagnetic metal layer are wider than awidth of the first ferromagnetic layer.
 6. The spin-orbit torque typemagnetization rotational element according to claim 1, whereinthicknesses of the first nonmagnetic metal layer and the secondnonmagnetic metal layer are thicker than a thickness of the spin-orbittorque wiring, and widths of the first nonmagnetic metal layer and thesecond nonmagnetic metal layer are wider than a width of the spin-orbittorque wiring.
 7. The spin-orbit torque type magnetization rotationalelement according to claim 1, wherein the first nonmagnetic metal layerand the second nonmagnetic metal layer include any one of a groupconsisting of Ag, Au, Cu, Al, W, Co, Ni, Zn, Ta, TiN, and TaN.
 8. Thespin-orbit torque type magnetization rotational element according toclaim 1, wherein the first nonmagnetic metal layer and the secondnonmagnetic metal layer are connected to a second surface on a sideopposite to a first surface facing the first ferromagnetic layer of thespin-orbit torque wiring.
 9. The spin-orbit torque type magnetizationrotational element according to claim 1, wherein the first nonmagneticmetal layer and the second nonmagnetic metal layer are connected to afirst surface facing the first ferromagnetic layer of the spin-orbittorque wiring.
 10. The spin-orbit torque type magnetization rotationalelement according to claim 1, wherein the first nonmagnetic metal layerand the second nonmagnetic metal layer are connected to the spin-orbittorque wiring without an intervening oxide.
 11. The spin-orbit torquetype magnetization rotational element according to claim 1, wherein aportion of the first ferromagnetic layer overlaps the first nonmagneticmetal layer or the second nonmagnetic metal layer in a plan view seen inthe second direction.
 12. The spin-orbit torque type magnetizationrotational element according to claim 11, further comprising a controlunit, which allows a read current to flow between the firstferromagnetic layer and one of the first nonmagnetic metal layer and thesecond nonmagnetic metal layer overlapping the portion of the firstferromagnetic layer in a plan view seen in the second direction.
 13. Aspin-orbit torque magnetoresistance effect element comprising: aspin-orbit torque type magnetization rotational element according toclaim 1; a nonmagnetic layer which faces a fourth surface on a sideopposite to a third surface facing the spin-orbit torque wiring in thefirst ferromagnetic layer; and a second ferromagnetic layer sandwichingthe nonmagnetic layer together with the first ferromagnetic layer.
 14. Amagnetic memory comprising a plurality of spin-orbit torque typemagnetoresistance effect elements according to claim
 13. 15. Thespin-orbit torque type magnetization rotational element according toclaim 1, wherein the second direction is perpendicular to the firstdirection.